The present invention generally relates to methods of fabricating substrates for microelectronics, optoelectronics, or optics involving transfer of a useful layer from a first support to a second support.
Various techniques have recently been developed to allow the mechanical transfer of a layer of semiconductor material from a first support to a second support. The layer may or may not have undergone component production treatments before the transfer. For example, one treatment uses buried porous layers that can be attacked chemically and has been described in U.S. Pat. No. 6,100,166. Another method utilizes substrates weakened by implanting gas species to obtain a thin useful layer that can be detached from the remainder of the material by fracture at the implanted zone. Lastly, molecular bonding techniques utilize a controlled bonding energy so that a mechanical force can result in detachment of a layer which has been temporarily bonded to a support.
When a useful layer is connected to a first support using one of the above techniques, transfer of the layer involves bringing a second support into contact with the free face of the useful layer using suitable bonding forces. The free face of the assembly including the useful layer and the first support is known as the “front” face. The transfer is completed by applying stress forces (typically tension and/or bending and/or shear forces) between the useful layer and the first support. One or more tools could be used to detach the useful layer, such as a drawing rig or a blade introduced laterally at the weakened interface to propagate a crack, or a jet of fluid can be applied to the weakened interface (see, for example, International Application Publication No. WO01/04933). When the useful layer has not undergone any component fabrication steps, then the transfer is generally carried out regardless of the bonding technique employed to affix the useful layer to the second support (such as by molecular bonding, eutectic bonding, bonding using a polymer or resin, etc).
However, if the useful layer has already undergone steps in the component fabrication process, then it is often necessary to carry out different types of deposition treatments (for example, semiconducting or semiconductive oxides or nitrides, polycrystalline semiconductor, amorphous semiconductor, monocrystalline semiconductor formed by homo-or hetero-epitaxy). For example, when a “full wafer” method is carried out in a specific reactor, the deposits have a tendency to partially or completely cover the free face of the useful layer and to overflow onto the side faces of the substrate that include the useful layer and the first support. Such an overflow produces a useful layer that is encapsulated resulting in a strengthening of the bond at the periphery between the useful layer and the first support. This condition can cause problems during the subsequent detachment step required to transfer the useful layer to the second support.